For more than a year, Rosemary McGinn's coworkers used to think she was drunk. Or crazy.

In reality, she had a rare tumor on her pancreas that was causing her blood sugar to plummet, starving her brain of fuel.

"What happened was I noticed a few times I would get weird," McGinn, a 54-year-old realtor from Rockland County, N.Y., told ABCNews.com. "I felt just not myself. I couldn't explain it to anybody else."

So around Easter 2011, her coworkers sent her home from work early, thinking she was drunk. That night, a client called to set up an appointment, but as soon as McGinn hung up, she forgot the time and place they'd just decided.

Not long after that, McGinn was driving with her husband when she forgot where she lived. She forgot who the president was and what year it was.

The next thing she knew, she was in her kitchen with two paramedics standing over her. They were feeding her candy and checking her blood sugar.

Normal blood sugar is between 70 milligrams per deciliter and 140 milligrams per deciliter, so most people feel symptoms of low blood sugar -- confusion, hunger and shakiness, for example -- when they hit about 60 milligrams per deciliter, said Dr. Ronald Tamler, who directs the Mount Sinai Diabetes Center in New York City and who would solve the medical mystery.

McGinn's blood sugar had dropped to 25 milligrams per deciliter, making her extremely hypoglycemic. Tamler said most people would pass out but McGinn didn't because her body had become so used to the frequent dips in blood sugar.

And doctors didn't know why it was happening considering that McGinn's insulin levels appeared to be normal. Insulin is the hormone that reduces blood sugar and allows the body to use that sugar for energy.

So for more than a year, McGinn never left house without candy and juice out of fear that she would have another episode. She gained 25 pounds.

But without warning, her blood sugar plummeted anyway. When her husband called her at work, she sometimes wouldn't pick up the phone, so he would call the front desk. Her coworkers would report back that McGinn was sitting at her desk, but in her own world, talking to no one in particular.

Another time she was standing with her husband and the next thing she knew, he was force-feeding her orange juice. He told her she began to talk about how she thought her hip might fall out, and he realized she was having an episode. McGinn said her hip didn't even hurt.

"I'd be having 3,000 different conversations with myself. It was scary," McGinn said. "I thought there's no way in hell I could live like this."

Finally, McGinn went to Mount Sinai and met Tamler. He figured it out: McGinn's insulin levels were normal, but only for a person who had recently eaten. When McGinn's blood sugar dropped, she was still producing those "normal" insulin levels, further decreasing her blood sugar.

"Some sugar needs to stay in the blood stream," Tamler said. "It acts as fuel for red blood cells. if the brain doesn't get enough sugar you're in real trouble."